Chapter 20. Superficial Face

Big Picture

The sensory innervation of the face is provided by the three divisions of the trigeminal nerve [cranial nerve (CN) V], with each division supplying the upper, middle, and lower third of the face. The facial artery and the superficial temporal artery provide vascular supply.

Cutaneous Innervation of the Face

The skin of the face and scalp is innervated by the cutaneous branches of the three divisions of CN V and by some nerves from the cervical plexus (Figure 20-1A and B).

• CN V-1 (ophthalmic nerve). Provides cutaneous innervation to the anterior region of the scalp via the supraorbital nerve and the supratrochlear nerve, the skin of the upper eyelid via the lacrimal nerve, and the bridge of the nose via the external nasal nerve and the infratrochlear nerve.
• CN V-2 (maxillary nerve). Provides cutaneous innervation to the skin along the zygomatic arch via the zygomaticofacial and the zygomaticotemporal nerves and the skin of the maxillary region, lower eyelid, and upper lip via the branches of the infraorbital nerve.
• CN V-3 (mandibular nerve). Provides cutaneous innervation to the skin of the lateral aspect of the scalp and the lateral part of the face, anterior to the external acoustic meatus, via the auriculotemporal nerve, the skin covering the mandible via the buccal nerve, and the skin of the lower lip via the mental nerve.
• Cervical plexus. The great auricular nerve (C2–C3) innervates the skin over the angle of the mandible just in front of the ear.

Vessels of the Face

The face has a very rich blood supply provided primarily from the following vessels (Figure 20-1C):

• Facial artery. Branches off the external carotid artery and courses deep to the submandibular gland; winds around the inferior border of the mandible, anterior to the masseter muscle, to enter the face. As it ascends in the face, the facial artery supplies most of the face by way of the inferior labial, superior labial, lateral nasal, and angular arteries.
• Supraorbital and supratrochlear arteries. Terminal branches of the ophthalmic artery, a branch of the internal carotid artery, which supply the anterior portion of the scalp.
• Superficial temporal artery. A terminal branch of the external carotid artery provides arterial supply to the lateral surface of the face and scalp.
• Facial vein. Formed by the union of the supraorbital and supratrochlear veins. The facial vein descends in the face and receives tributaries corresponding to the branches of the facial artery. The facial vein drains into the internal jugular vein.

Big Picture

Muscles of facial expression are located in the superficial fascia, and as their name implies, they control facial expression. The muscles of facial expression are innervated by the facial nerve (CN VII).

Muscles of Facial Expression

The muscles of facial expression are voluntary muscles located in the superficial fascia. In general, they arise from bones or fascia of the skull and insert into the skin, which enables a wide array of facial expression. The muscles are sometimes indistinct at their borders because they develop embryologically from a continuous sheet of musculature derived from the second branchial arch. The muscles of facial expression are located superficially in the neck, face, and scalp. Each muscle is innervated by CN VII (except the muscles of mastication, which are innervated by CN V-3).

The muscles of facial expression can be organized into the following groups (Figure 20-2A):

• Scalp and forehead (see Chapter 15)
  • Frontalis. Connects with the occipitalis muscle by a cranial aponeurosis (galea aponeurotica); and wrinkles the forehead.
• Muscles of the orbit
  • Orbicularis oculi. Consists of orbital and palpebral portions, forming a sphincter muscle that closes the eyelids.
  • Corrugator supercilii. Located deep to the orbicularis oculi; draws the eyebrows medially.
• Muscles of the nose
  • Procerus. Wrinkles the skin over the root of the nose.
  • Nasalis and levator labii superioris alaquae nasi. Flare the nostrils.
• Muscles of the mouth
  • Orbicularis oris. Originates from the bones or fascia of the skull and inserts in the substance of the lips, forming an oral sphincter.
  • Levator labii superioris and levator anguli oris. Raise the upper lip.
  • Zygomaticus major and minor. Raise the corners of the mouth (smile).
  • Risorius. Draws the corners of the lips laterally.
  • Depressor labii inferioris and depressor anguli oris. Lower the bottom lip.
  • Buccinator. Compresses the cheek when whistling, blowing, or sucking; holds food between the teeth during chewing.
• Neck
  • Platysma. Tenses the skin of the neck and lowers the mandible. Primarily located in the neck, although it does have attachments in the lower mandible and corners of the mouth.

Motor Nerve Supply to the Face

CN VII provides motor innervation to the muscles of facial expression (Figure 20-2B). The facial nerve exits the skull through the stylomastoid foramen and immediately gives off the posterior auricular nerve and other branches that supply the occipitalis, stylohyoid, and posterior digastricus muscles and the posterior auricular muscle. CN VII courses superficial to the external carotid artery and the retromandibular vein, enters the parotid gland, and divides into the following five terminal branches: temporal, zygomatic, buccal, mandibular, and cervical nerves, which in turn supply the muscles of facial expression. Other muscles of the face include muscles of mastication (temporalis, masseter, and the medial pterygoid and lateral pterygoid muscles), which are innervated by the motor division of CN V-3.

Big Picture

The parotid gland is situated in the lateral part of the face on the surface of the masseter muscle, anterior to the sternocleidomastoid muscle. A dense fascia covers the gland. The parotid gland produces and secretes saliva into the oral cavity and is innervated by visceral motor parasympathetic fibers from the glossopharyngeal nerve (CN IX).

Parotid Duct

The parotid duct crosses the masseter muscle, pierces the buccinator muscle, and opens into the oral cavity adjacent to the second upper molar (Figure 20-3A).

Structures Associated with the Parotid Gland

• Motor branches of CN VII. CN VII exits the stylomastoid foramen, enters the posterior surface of the parotid gland, and courses through the gland en route to innervate the muscles of facial expression. CN VII also provides visceral motor innervation to all glands of the head, with the only exception being the parotid gland, the gland that you would think CN VII would innervate (Figure 20-3A and B).
• Retromandibular vein. The superficial temporal vein and the maxillary vein join to form the retromandibular vein within the parotid gland and exit its inferior border, where the retromandibular vein bifurcates into anterior and posterior divisions. The anterior division joins with the facial vein to become the common facial vein, which enters the internal jugular vein. The posterior division joins with the posterior auricular vein, forming the external jugular vein.
• External carotid artery. The common carotid artery bifurcates at the level of the thyroid cartilage into the external and internal carotid arteries. The external carotid artery enters the inferior border of the parotid gland and within the gland divides into the superficial temporal artery and the maxillary artery. Both arteries emerge from the anterosuperior border and provide vascular supply to the temporal fossa and scalp (superficial temporal artery) and the deep face (maxillary artery).

Innervation of the Parotid Gland

The parotid gland is innervated by visceral motor neurons from CN IX (Figure 20-3C).

• Preganglionic parasympathetic neurons from CN IX originate in the inferior salivatory nucleus of the medulla and exit the jugular foramen along with the vagus nerve (CN X) and the spinal accessory nerve (CN XI).
• A branch of CN IX, the tympanic nerve, re-enters the skull via the tympanic canaliculus, enters the middle ear, and forms the tympanic plexus.
• CN IX gives rise to the lesser petrosal nerve, which exits the middle ear and the skull via the foramen ovale to synapse in the otic ganglion.
• Postganglionic parasympathetic neurons exit the otic ganglion and then “hitch-hike” along the auriculotemporal nerve en route to the parotid gland.